1. Field of the Invention
The present invention relates generally to electronic devices, and more specifically to fabrication of system subassemblies such as memory boards and memory modules.
2. Description of the Prior Art
Assembly and test of computer subsystems, such as memory modules and subsystems, can add a significant percentage to the cost of completed computers. It is important to complete the assembly and testing of subassemblies in a cost efficient manner in order to keep production prices for the subassemblies low enough for them to be sold at competitive prices.
With some systems, the integrated circuit devices which are used are not guaranteed to have a 100% incoming functionality. For example, it has been proposed to provide personal computer memory subsystems which are designed to use memory chips which are partially nonfunctional, and use error detection and correction circuitry to compensate for chip defects. An example of such a proposed subsystem is described in detail in co-pending patent application Ser. No. 07/722,937 titled MEMORY SUBSYSTEM.
It is known that integrated circuits generally tend to have a high percentage of failures very early in the lifetime of the devices. This phenomena is often referred to as infant mortality. Since a significant percentage of parts fail in a short period of time, it is common to subject integrated circuit devices to relatively severe operating conditions for a short period of time in order to force these infant mortality failures to occur. This process is often referred to as burn-in. Proper burn-in tends to be somewhat expensive because of the large number of test fixtures required, but can virtually eliminate failures of integrated circuit devices within the first few years of their operating lifetime. Parts which survive burn-in tend to function for a significant fraction of their expected device lifetime.
In the case of partially nonfunctional devices, such as the memory devices described above, the integrated circuit chips generally have not been subjected to burn-in. These chips were generally rejected at the wafer probe stage. Therefore, a system which makes use of such devices is preferably subjected to burn-in test procedures in order to find and remove devices easily subject to complete failure.
It would be desirable to provide a technique which helps minimize the overall assembly and test time and expense for subsystem assembly and burn-in. Such a system preferably provides a relatively high degree of parallelization during burn-in, and the ability to individually test the integrated circuit devices.